The pharmacokinetics and pharmacodynamics of selected corticosteroids--particularly prednisone and prednisolone--are examined in relation to age, disease, and physiological factors governing their disposition. A sensitive and specific high performance liquid chromatographic assay has been developed for measuring low concentrations of multiple steroids in biological fluids. Experimental dialysis and computer methods for determining steroid binding to corticosteroid binding globulin and albumin allow assessment of the role of protein binding. Prednisolone pharmacokinetics are examined in normal subjects to address bioavailability and dose-dependence. Studies in patients include pediatric and adult subjects with asthma who are typical, resistant, or toxic in relation to prednisone therapy. Children with nephrotic syndrome allow evaluation of drug-disease interactions. Prednisolone distribution into breast milk and disposition in pregnant women with asthma receiving prednisone therapy are also examined. Animal models are being evaluated to more intensely assess mechanisms of nonlinear steroid disposition. Pharmacokinetic and statistical methodology will be evolved to optimize data analysis and account for the pronounced nonlinear distribution and clearance processes in normal and diseased subjects.